upgrade_jenkins.sh

#! /bin/sh

# directory that contains the jenkins.war
JENKINS_WAR_DIR=/usr/share/jenkins

# Absolute path the jenkins.war
JENKINS_WAR=${JENKINS_WAR_DIR}/jenkins.war

# Absolute path the jenkins.war for backup
JENKINS_BACKUP_WAR=/tmp/jenkins.war.bak

# latast jenkins.war 
JENKINS_LATEST_WAR_URL=http://updates.jenkins-ci.org/latest/jenkins.war

# Absolute path the downloaded jenkins.war
DOWNLOADED_WAR=${WORKSPACE}/jenkins.war

# backup
rm -f ${JENKINS_BACKUP_WAR}
cp ${JENKINS_WAR} ${JENKINS_BACKUP_WAR}

# get latest war 
rm -f ${DOWNLOADED_WAR}
wget ${JENKINS_LATEST_WAR_URL} --no-check-certificate

# replace to the new war 
rm -f ${JENKINS_WAR}
cp ${DOWNLOADED_WAR} ${JENKINS_WAR}

#safe restart
service jenkins restart